Methodology Discrepancy and Data Comparability of Greenhouse Gas Monitoring from Water Resource Recovery Facilities

Wastewater is a major source of methane (CH₄) and nitrous oxide (N₂O), highlighting the need for accurate monitoring to develop accurate inventories and effective mitigation strategies. This study systematically evaluates current measurement methodologies, emphasizing significant variability across different techniques that contribute to reporting discrepancies. Bottom-up approaches, such as flux chambers and <i>in situ</i> liquid sensors, dominate unit-level data collection, while emerging top-down methods provide plant-level-integrated estimates. No inherent bias was identified across methodologies, but the choice of techniques was influenced by the treatment processes and operational conditions. When multiple methods were applied at the same site, calibrations were needed between emission factors derived from the dissolved and gaseous concentrations. Data scarcity hinders inventory building for sewers, distributed systems, and facility-level analysis. This study offers a comprehensive review of current monitoring practices and proposes a framework to address the data gaps and inconsistencies. By advocating for harmonized methodologies, the framework seeks to enhance data comparability and reliability by integrating available approaches while promoting more comprehensive data reporting to facilitate meta-analyses and cross-contextual evaluations.